Substituted cyanamide-accelerated tetraethyl lead process



United States Patent 3,412,123 SUBSTITUTED CYANAMIDE-ACCELERATED TETRAETHYL LEAD PROCESS David John Klinke, Salem, N.J., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Apr. 27, 1966, Ser. No. 545,551 6 Claims. (Cl. 260-437) This invention relates to the manufacture of tetraethyl lead and more particularly to the reaction of ethyl chloride and sodium-lead alloy in the presence of a substituted cyanamide.

Tet-raethyl lead has been made commercially for years by the reaction of ethyl chloride and monosodium-lead alloy usually in the presence of an accelerator such as an aldehyde, ketone, ester, carboxamide or acetal. These accelerators increase the rate of reaction so that the ultimate conversion can be achieved in a shortened period of time.

In US. Patent No. 2,653,159, Beste et al., disclose a process for producing tetraethyl lead in which a sodiumlead alloy containing 80 to 86.5% by weight lead is reacted with ethyl chloride in the presence of accelerators such as certain ketones, aldehydes, esters, alcohols and amines. They indicate that without an accelerator this reaction is so slow that essentially no conversion is obtained after 3 hours. Beste et al. further disclose that amides and nitriles are detrimental and should be avoided.

It is an object of this invention to provide a new process for producing tetraethyl lead by the reaction of ethyl chloride with sodium-lead alloys. Another object is to provide a new accelerator for this process. These and other objects will become apparent from the following description of this invention.

It has now been discovered that the above objects can be accomplished by reacting ethyl chloride in the liquid phase with a sodium-lead alloy containing to by weight sodium and 80 to 90% by weight lead at a temperature of 80 to 130 C. in the presence of 0.001 to 0.1 mole, per gram atom of sodium in the alloy, of a substituted cyanamide of the formula in which each R is hydrogen or an aliphatic hydrocarbon radical having 1 to 4 carbon atoms, and R is an alklene radical having 2 to 3 carbon atoms. Using the substituted cyanamide accelerators of this invention, results equivalent to or in some cases superior to those obtained in the case of prior art accelerators are obtained. The suitability of the above-described substituted cyanamides as accelerators for this process is quite surprising particularly in view of the teaching in the Beste et al. patent that nitriles are detrimental and should be avoided.

In accordance with the present invention, ethyl chloride and sodium-lead alloy are reacted in the presence of the accelerator. The sodium-lead alloy used in the process should contain about 80 to 90% by weight lead and about 10 to 20% by weight sodium. This range covers monosodium-lead alloy of the formula NaPb which contains 10% sodium and 90% lead, sodium-lead alloy of the formula Na Pb which contains 20% sodium and 80% lead, and mixtures thereof. The alloy may "be used in various forms, usually comminuted, such as by grinding, flaking, or quenching in ethyl chloride.

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The substituted cyanamides used as accelerators in the process of this invention are those of the formula in which each R is hydrogen or an aliphatic hydrocarbon radical having 1 to 4 car-bon atoms, and R is an alkylene radical having 2 to 3 carbon atoms. The aliphatic hydrocarbon radicals may be saturated or unsaturated, straight or branched-chain radicals. Preferably, these radicals are n-alkyl groups. Typical examples of suitable substituted cyanamides include dimethyl cyanamide, methylethyl cyanamide, diethyl cyanamide, di-npropyl cyanamide, di-n-butyl cyanamide, di-iso-butyl cyanamide, di-n-pentyl cyanamide, di-iso-sentyl cyanamide, diallyl cyanamide and dipropargyl cyanamide. Suitable cyclic cyanamides include tetramethylene cyanamide and pentamethylene cyanamide. Dimethyl cyanamide is particularly preferred since it gives the best result of the substituted cyanamides and is superior to acetone, the prior art accelerator most commonly used in commercial operations.

The amount of ethyl chloride employed may be varied over wide limits. In general, it will range from about 1 to 50 moles of ethyl chloride per grame atom of sodium in the alloy, and preferably about 2 to 15 moles per gram atom of sodium. When less than about 1 mole of ethyl chloride per gram atom of sodium is employed, the expensive alloy is not used efficiently. The use of more than about 15 moles of ethyl chloride per gram atom of sodium does not provide any particular benefit, although larger amounts up to about 50 moles can be used, if desired. Most preferably about 3 to 10 moles of ethyl chloride are used per gram atom of sodium. Ethyl chloride sources which are normally satisfactory for ethylating sodium-lead alloys as in the conventional acetone-ac celerated processes are also suitable for use in the process of this invention.

The amount of di-substituted cyanamide employed may vary from about 0.001 to 0.1 mole per gram atom of sodium in the alloy. Preferably about 0.005 to 0.05 mole per gram atom of sodium is employed.

The reaction should be carried out at a temperature of to 130 C. At temperatures below about 80 C. the reaction does not generally proceed at any practical rate. Temperatures above about 130 C. should be avoided since they are unnecessary, require high pressure equipment and are potentially hazardous. Preferably, temperatures of about to C. are employed.

It is necessary that the reaction be carried out under sufficient pressure to maintain the ethyl chloride in the liquid phase or under reflux. In general, pressures of about 80 to 550 p.s.i.g. are employed. Most commonly the reaction is carried out in a closed reaction vessel under autogenous pressure which is generally in the range of about 150 to 400 p.s.i.g.

The overall process of this invention comprises mixing alloys with the ethyl chloride and the substituted cyanamide, holding such mixture in a closed reaction vessel under agitation at a temperature in the range of 80 to C., at which temperature reaction begins and proceeds at a reasonable rate, and recovering the tetraethyl lead from the reaction mass. The reactants and substituted cyanamide may 'be introduced separately or together, all at once or gradually during the course of the reaction. The substituted cyanamide may be added as such or in a suitable carrier which conveniently may be ethyl chloride.

The reaction components may be mixed at temperatures below those at which the reaction proceeds at a substantial rate, for example, below C. and the mixture then brought to operating temperature. Alternatively, the reactants and other essential components may be mixed at temperatures within the reaction range. The reaction may be conducted batch-wise or continuously.

The resulting reaction product may be worked-up in the conventional way known to those skilled in the art. Normally, the product mass temperature is adjusted to about 25 to 60 C. and the residual ethyl chloride is vented from the reaction vessel and passed through a recovery system as in conventional tetraethyl lead processes. The tetraethyl lead is then recovered by solvent extraction or by steam distillation according to wellknown techniques.

The following examples, illustrating the novel process disclosed herein, are given without any intention that the invention be limited thereto. All parts and percentages are by weight.

Examples 1 to Na Pb alloy process Crushed sodium-lead alloy (100 parts) having the empirical formula, Na Pb enclosed in a glass ampoule, and quantities of substituted cyanamides as indicated in Table I are charged to a steel bomb. The bomb is cooled to the temperature of solid CO and 310 parts of ethyl chloride (5.5 moles/g. atom Na) are added under a nitrogen atmosphere; this corresponds to a loading density of 0.17 g. of ethyl chloride per cc. of bomb capacity. The bomb is closed, struck sharply against a solid object to break the arnpoule containing the alloy, immersed in a 110 C. heating bath, and shaken vigorously at this temperature for 1 hour. The bomb is then cooled to 60 C. to stop the reaction and opened. Its contents are analyzed for tetraethyl lead yield based on both Na and Pb charged as alloy.

For comparison, a control experiment is carried out in which no accelerator is used. A summary of the variables and results is given in the following table.

TABLE I The procedure of Examples 1 to 5 is repeated except that 0.026 mole per gram atom of sodium of tetramethylene cyamamide is used as accelerator. The result is similar to that obtained in Example 4.

Examples 7 and 8NaPb alloy process Using the procedure of Examples 1 to 5, monosodiumlead alloy is reacted with ethyl chloride (5.5 moles/g. atom Na) using either dimethyl cyanamide or diethyl cyanamide as the accelerator in separate runs. The reaction is carried out for 1 hour at 110 C. The following results are obtained.

TABLE II Accelerator Yield, percent Example Accelerator 00110., mole/g. based on atom Na.

Na Pb 7 (CH=)NCN .008 90 22. 5 8 (CzHmNCN .024 86 21. 5

Example 9 The procedure of Examples 7 and 8 is repeated except that .024 mole per gram atom of sodium of penta'methylene cyanamide is used as accelerator. The result is similar to that obtained in Example 8.

Although the invention has been described and exemplified by way of specific embodiments, it is to be understood that it is not limtied thereto. As will be apparent to those skilled in the art, numerous modifications and variations of these embodiments may be made without departing from the spirit of the invention or the scope of the following claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for making tetraethyl lead which comprises reacting ethyl chloride in liquid phase with a sodium-lead alloy containing from 10 to 20% by weight sodium and to 80% by weight lead at a temperature of 80 to C., in the presence of 0.001 to 0.1 mole, per gram atom of sodium in the alloy, of a substituted cyanamide of the formula RC H: /CH2 N-CEN or R N-CEN R CH2 CH2 in which each R is hydrogen or an aliphatic hydrocarbon radical having 1 to 4 carbon atoms, and R is an alkylene radical having 2 to 3 carbon atoms.

2. The process of claim 1 in which the substituted cyanamide is of the formula N-CE RCH:

References Cited UNITED STATES PATENTS 2,464,399 3/1949 Clem 260437 2,635,106 4/1953 Shapiro et al. 260-437 2,635,107 4/1953 Tanner 260437 2,653,159 9/1953 Beste et a1. 260437 TOBIAS E. LEVOW, Primary Examiner.

H. M. S. SNEED, Assistant Examiner. 

1. A PROCESS FOR MAKING TETRAETHYL LEAD WHICH COMPRISES REACTING ETHYL CHLORIDE IN LIQUID PHASE WITH A SODIUM-LEAD ALLOY CONTAINING FROM 10 TO 20% BY WEIGHT SODIUM AND 90 TO 80% BY WEIGHT LEAD AT A TEMPERATURE OF 80* TO 130*C., IN THE PRESENCE OF 0.001 TO 0.1 MOLE, PER GRAM ATOM OF SODIUM IN THE ALLOY, OF A SUBSTITUTED CYANAMIDE OF THE FORMULA 